Maintenance; Trouble Analysis - Lambda LJS-13A Series Instruction Manual

MAINTENANCE
GENERAL
This section describes trouble analysis routine, calibration and test procedures that are useful for —
servicing the Lambda power supply. A trouble chart is provided as an aid for the troubleshooter. Refer
to the section on SPECIFICATIONS AND FEATURES for the minimum performance standards.
TROUBLE ANALYSIS
Whenever trouble occurs, systematically check all fuses, primary power lines, external circuit elements,
and external wiring for malfunction before troubleshooting the equipment. Failures and malfunctions often
can be traced to simple causes such as improper jumpers and supply-load connections or fuse failure due to
metal fatigue.
CHECKING TRANSISTORS AND CAPACITORS
Check transistors with an in-circuit transistor checker. If no checker is available, transistors can be
checked with an ohmmeter that has a highly limited current capability. Observe proper polarity for PNP
or NPN to avoid error in measurement. The forward transistor resistance is low but never ZERO; back-
ward resistance is always higher than the forward resistance.
Do not assume trouble is eliminated when only one part is replaced. This is especially true when one
transistor fails, causing other transistors to fail. Replacing only one transistor and turning power on, before
checking for additional faulty components could damage the replaced component.
When soldering semi-conductor devices, hold the lead being soldered with a pair of pliers or a commer-
cial heat sink device placed between the component and the solder joint.
NOTE: The leakage resistance obtained from a simple resistance check of a capacitor is not always
an indication of a faulty capacitor. In all cases the capacitors are shunted with resistances, some of
which have low values. Only a dead short is a true indication of a shorted capacitor.
PRINTED CIRCUIT BOARD MAINTENANCE TECHNIQUES
1. If foil is intact, but not covered with solder, it is a good contact. Do not attempt to cover with solder.
2. Voltage measurements can be made from either side of the board. Use a needle-point probe to penetrate
to the wiring whenever a protective coating is used on the wiring. A brass probe can be soldered to an
alligator clip adapted to measuring instrument.
3. Always use a heat sink when soldering transistors; a transistor pad with mounting feet is an effective
heat sink.
4. Broken or damaged printed wiring is usually the result of an imperfection, strain or careless soldering.
To repair small breaks, tin a short piece of hook-up wire to bridge the break, and holding the wire in
place, flow solder along the length of wire so that it becomes part of the circuitry.
3. When unsoldering components from the board never pry or force loose the part; unsolder the component
by using the wicking process described below:
a) Select a 3/16 inch tinned copper braid for use as a wick; if braid is not available, select AWG No. 14
or No. 16 stranded wire with 1/2 inch insulation removed.
IM-LJS-13A